Ethylene polymer useful as a lubricating oil viscosity modifier E-25

ABSTRACT

An ethylene ter- or tetrapolymer useful as a viscosity modifer and a process for preparing the polymer. The polymer comprises ethylene, an alpha-olefin, a non-conjugated diene and, optionally, a cationically polymerizable monoolefin. The polymerization catalyst comprises a Ziegler catalyst in conjunction with a cationic polymerization catalyst.

This is a division of application Ser. No. 682,286, filed 12/17/84, nowU.S. Pat. No. 4,575,574.

BACKGROUND OF THE INVENTION

It is well known that refined petroleum oils generally exhibitsubstantial changes in viscosity with temperature. The viscosity index("V.I.") is a measure of the slope of the temperature-viscosity curve.It is preferred that a lubricating oil, e.g., automobile lubricatingoil, exhibit a "flat" V.I. curve. The desired V.I. characteristic isgenerally achieved by adding oil soluble polymers to oil. For many yearsthe preferred polymer additive was polyisobutylene.

Recently, specialty ethylene-propylene copolymers have been developedand are now widely used as V.I. improvers. Since lubricating oils areused in a wide range of applications, the market requires a variety ofgrades of such polymers having differing degrees of "thickening effect"so as to permit the formulation of lubricating oils having differentviscosities and "Shear stability indicies". Such polymer grades may beprepared by direct synthesis, the molecular weight grades beingdetermined by the polymerization process, or the different molecularweight grades can be produced by degradation of an ethylene-propylenecopolymer so as to produce lower molecular weight fractions.

The patent literature is replete with many publications dealing withethylene ter-and tetrapolymers containing one or more types of dienesintroduced for a variety of reasons including a means for introducingunsaturation, thereby providing a means for crosslinking the polymer.

In the case of viscosity index improvers, crosslinking is neither anecessary nor desirable characteristic of the polymer. Illustrative ofpatents dealing with unsaturated ethylene ter-and tetrapolymers is U.S.Pat. No. 3,790,480. Polymers of ethylene, C₃ -C₁₈ higher alpha olefinsand two classes of dienes are taught, the dienes having double bonds ofthe same or different polymerizability. In one class of dienesrepresented by 1,4-hexadiene, only one of the double bonds is readilypolymerizable by the catalyst used. In another class of which2,5-norbornadiene is representative, both double bonds are polymerizableutilizing the polymerization process of the patent. It is taught thatthe preferred viscosity indexes improvers are ethylene tetrapolymerswherein both classes of double bonds are used.

Presumably, superior properties are achieved because use of a diene withtwo active double bonds results in long chain branching with aconcomitant increase in bulk viscosity of the polymer without anysignificant increase in intrinsic viscosity or thickening efficiency.Increased bulk viscosity facilitates the manufacture and storage of thepolymer. The catalyst used for polymerization is a Ziegler typecatalyst. Both double bonds of the 2,5-norbornadiene are polymerizableby the Ziegler catalyst. The other diene, 1-4 hexadiene, however, hasonly one Zeigler catalyst polymerizable double bond. Hence, the polymersinclude a minor amount of unsaturation.

Unsaturation in a polymeric viscosity index improving oil additive isgenerally undesirable since the unsaturated moiety introduces a sitethrough which chemical reactions can occur under the conditions of useof the lubricating oil. Such reactions are undesirable since they causechanges in the viscosity of the lubricating oil. On the other hand,branched saturated ethylene tri or tetra polymers have desirableproperties as viscosity modifiers.

SUMMARY OF THE INVENTION

It has surprisingly been found that substantially saturated, long chain,branched ter-and tetrapolymers of ethylene can be prepared using anon-conjugated diene polymer by selecting as the polymerizationinitiator a catalyst system which is both a coordination catalyst and acationic polymerization catalyst. The preferred coordination catalystsare Ziegler catalysts known to be useful in the preparation ofethylene-propylene-non-conjugated diene terpolymers. The cationicpolymerization catalysts are either conventional cationic polymerizationcatalysts or are catalyst species which, in conjunction with thecoordination catalyst, initiate cationic polymerization.

The preferred monomers are ethylene propylene and5-ethylidene-2-norbornene. The preferred catalyst system is VCl₄ orVOCl₃, in combination with Al₂ Cl₃ Et₃.

DETAILED DESCRIPTION

This invention relates to a polymer comprising the reaction product ofethylene, an alpha-olefin and a non-conjugated diene which has utilityas a viscosity modifier. More particularly it relates to saturatedter-and tetra polymers of ethylene, an alpha olefin and at least onenon-conjugated diene wherein the diene has a first double bondpolymerizable in the presence of a coordination catalyst and a seconddouble bond which is cationically polymerizable

Not wishing to be bound by theory, it is believed that a polymer of theethylene, alpha-olefin and non-conjugated diene is formed wherein thecoordination catalyst polymerizable diene is incorporated into thebackbone with subsequent coupling of these chains involving thecationically polymerizable double bond. This coupling produces a longchain branch in the polymer molecule. Of course, it is probable thatsome degree of simultaneous reaction of both double bonds occurs.However, since only small quantities of non-conjugated diene is used, ascompared to ethylene and other alpha olefins, the mass effect mitigatesin favor of its incorporation into the backbone first. In any event, theresultant polymer is a predominately saturated, long chain, branched oilsoluble polymer of high bulk viscosity and low intrinsic viscosity.

The alpha-olefins suitable for use in the practice of this invention arelinear and branched C₃ -C₁₈ alpha-olefins. The preferred alpha-olefinsare C₃ -C₈ linear alpha-olefins. The most preferred alpha-olefin ispropylene.

Illustrative non-limiting examples of such alpha-olefins are propylene,butene, pentene, hexene, heptene, octene, nonene, decene, dodecene,2-methyl butene-3, 2-methyl pentene-4, 2-methyl hexene-5, 2-ethylhexene-5 etc.

The dienes suitable for use in the practice of this invention arenon-conjugated dienes having one double bond which is coordinationcatalyst polymerizable and one double bond which is cationicallypolymerizable. Illustrative non-limiting examples of such non-conjugateddienes are 2-methyl hexadiene-1,5; 2-methyl heptadiene-1,6;5-methylene-2-norbornene, 5-ethylidene-2-norbornene, 2-methylnorbornadiene, 5-isopropenyl-2-norbornene, 5-methallyl-2-norbornene,5(2'-methyl-1-propene)-2-norbornene, 5-methyl vinyl-2-norbornene,3-methallyl cyclopentene, and 3(2'-methyl-1-propenyl)cyclopentene anddicyclopentadiene.

A fourth monomer which is a cationically polymerizable monoolefin suchas isobutene may be included in the polymerization medium. All of themonomers must be hydrocarbons.

The polymerization is advantageously carried out in solution. Suitablesolvents for the polymerization reaction are hydrocarbon or chlorinatedhydrocarbon solvents which are solvents for both the polymer andmonomer. Illustrative examples of such solvents are hexane, methylcyclohexane, cyclohexane, pentane, isopentane, heptane,tetrachloroethylene, toluene, benzene, and so forth.

The catalyst system of this invention comprise (1) a coordinationcatalyst and (2) a catalyst which is a cationic polymerization initiatoror (3) a compound which in conjunction with (1) or (2) generates acationic catalyst. Illustrative examples of the coordination catalyst ofthis invention are those catalysts known generally as Ziegler catalysts.These Zeigler catalyst comprise, for example, VCl₄, VOCl₃, or VO(OR)₃wherein R is a hydrocarbon of 1 to 8 carbon atoms, e.g.,trialkoxyvanadate, in conjunction with a cocatalyst wherein thecocatalyst is an aluminum alkyl i.e., AlR₃ wherein R is as previouslydefined, or an alkyl aluminum halide in which the number of alkyl groupsis equal to or greater than the number of halogens, i.e., R_(m) Al_(n)X_(p) wherein X is halogen, R is as previously defined, n is an integer,m+p=3n and m≧p, e.g., Et₃ Al₂ Cl₃ or Et₂ AlCl.

The terms "cationic initiator" as used in the specification and claimsmeans a catalyst which at least to some degree, initiates cationicpolymerization. It may be necessary to improve the catalyst efficiencyby using a cationic promoter with the cationic initiator. Suitablecationic initiators are HCl, AlCl₃ or an alkyl aluminum halide in whichthe number of halogens is greater than the number of alkyl groups, i.e.,R_(r) Al_(s) X_(t), wherein R and X are as previously defined and r, s,and t are integers of positive values and r=3s-t, for example, EtAlCl₂.The cationic initiator is optionally utilized in conjunction with acationic promoter which is for example a tertiary alkyl halide, a benzylchloride or a benzyl bromide. Illustrative examples of the tertiaryalkyl halide are tertiary butyl chloride, 2-ethyl-2-chloro propane,2-methyl-2-chlorohexane, and so forth.

As described herein the catalyst system of this invention comprises acoordination catalyst in conjunction with a catalyst which initiatescationic polymerization which comprises either a cationic initiator or acationic initiator plus a promoter. While it will be readily recognizedthat the cationic promoters of this invention, alone, are never cationicpolymerization catalysts by themselves when used in conjunction withparticular cocatalysts of the Ziegler catalyst they can initiatecationic polymerization.

As used in the specification and claims, the term "cationicpolymerization catalyst" means (1) a catalyst which of itself initiatescationic polymerization, e.g., cationic initiator (2) a cationicinitiator which in conjunction with a cationic promoter exhibitsimproved catalytic activity, and initiates cationic polymerization or(3) a cationic promoter which in conjunction with the cocatalyst of aZiegler catalyst initiates cationic polymerization.

Where the cationic initiator is AlCl₃ or RAlX₂ where X is chlorine orbromine, a cationic promoter is not required, but may be used to improvecationic activity. Where the cocatalyst of the Ziegler catalyst is analkyl aluminum halide, as defined, e.g. Et₃ Al₂ Cl₃, the cationicpromoter alone in conjunction with the appropriate Ziegler catalyst is asuitable catalyst system to initiate both polymerization reactions.

In the Ziegler catalyst the ratio of co-catalyst to catalyst is definedin terms of the mole ratio Al/M wherein M is V or Ti. Al/M is about 2 toabout 25, preferably about 3 to about 15, more preferably about 4 toabout 7, e.g., 5.

The molar ratio of cationic initiator to Ziegler catalyst is about 0.1to about 20, preferably about 0.5 to about 15, more preferably about 1to about 10, most preferably about 2 to about 8, e.g., 3.

The amount of cationic promoter is based on the amount of cocatalyst orcationic initiator used and hence, is defined by the ratio P/Al whereinP represents the cationic promoter P/Al can be about 0.1 to about 10,preferably about 0.3 to about 5, more preferably about 0.5 to about 2,e.g. 1.

Table I presents non-limiting, illustrative examples of the catalystsystem of this invention.

                  TABLE I                                                         ______________________________________                                                                      Initi-                                          Ziegler Catalyst     Cationic ator*                                                                              Catalyst                                   Catalyst                                                                             Co-Catalyst                                                                             Al/M    Initiator                                                                            I/M  Promoter                                                                             P/Al                              ______________________________________                                        VCl.sub.4                                                                            Et.sub.3 Al.sub.2 Cl.sub.3                                                              5       HCl    3    --     --                                "      AlEt.sub.3                                                                              5       HCl    4    --     --                                "      Et.sub.3 Al.sub.2 Cl.sub.3                                                              5       --     --   t-butyl                                                                              5                                                                      chloride                                 VOCl.sub.3                                                                           Et.sub.2 AlCl                                                                           5       HCl    4                                             "      Al.sub.2 Et.sub.3 Cl.sub.3                                                              5       HCl    --   --     --                                "      Al.sub.2 Et.sub.3 Cl.sub.3                                                              8       EtAlCl.sub.2                                                                         --   benzyl 2                                                                      chloride                                 "      Et.sub.2 AlCl     HCl    6    --     --                                "      Et.sub.2 AlCl     EtAlCl.sub.2                                                                         --   t-butyl                                                                              2                                                                      chloride                                 "      Al.sub.2 Et.sub.3 Cl.sub.3                                                              5       EtAlCl.sub.2                                                                         3    t-butyl                                                                              1                                                                      chloride                                 "      Al.sub.2 Cl.sub.3 Et.sub.3                                                              5       EtAlCl.sub.2                                                                         --   --     --                                ______________________________________                                         *Ratio of cationic initiator to M.                                       

As used in the specification and claims the term "Thickening Efficiency"(T.E.) means the ratio of the weight percent of a polyisobutylene havinga Staudiger molecular weight of 20,000, required to thicken a solventextracted neutral mineral lubricating oil, having a viscosity of 150 SUSat 37.8° C., a viscosity index of 105 and an ASTM pour point of 0° F.,to a viscosity of 12.4 centistokes at 98.9° C., to the weight percent ofa test copolymer required to thicken the same oil to 12.4 centistokes at98.9° C.

Mooney Viscosity measures were performed in accordance with ASTM D-1646(ML 1+8 (100° C.)).

The term "shear stability index" (SSI) as used in the specification andclaims means the percent reduction of the polymer viscosity after it issubjected to sonic breakdown. The viscosity of the polymer is determinedbefore and after exposure to sonic breakdown and the SSI is recorded asthe percent reduction in viscosity.

The advantages of the instant invention may be more readily appreciatedby reference to the following examples:

EXAMPLE I

A solution polymerization is carried out in a continuous flow stirredreactor in the manner shown in Table II, Run A. The polymer formed had asufficiently low molecular weight, and thus thickening efficiency, sothat it had a shear stability index ("SSI") of 18% as compared to 30%for conventional ethylene propylene copolymers having a thickeningefficiency ("T.E.") of about 2.8. The bulk viscosity of the polymer wasmeasured at a stress of about 10⁴ dynes/cm². Measurements were performedat 100° C. using procedures as described in W. Graessley, G. Ver Strate,Rubber Chem & Tech, 53 842 (1980) incorporated herein by reference. Astrip of polymer (1×10×1.2 cm) is clamped at one end and allowed toextend under gravitational stress. The extension rate (dl/dt) iscalculated as a function of the density and Newtonian viscosity, and itis assumed that Troucons Rule, 3.sub.η shear=η elongation applies. Thebulk viscosity of the polymer was found to be a typical value for anethylene-propylene-5-ethylidene-2-norbornene terpolymer of the samemolecular weight, i.e. 4×10⁵ poise Table III. This bulk viscosity is toolow to permit satisfactory processing in a commercial elastomer plant.Such polymers exhibit such severe cold flow problems that the polymerrapidly agglomerates as a single solid mass and is not readily removedfrom the recovery vessels.

                  TABLE II                                                        ______________________________________                                                       Run #                                                          Process Variable A        B        C                                          ______________________________________                                        Residence Time min                                                                             17       15       13                                         Temperature °C.                                                                         27       27       27                                         Pressure Kpa     413      413      413                                        Total hexane feed kg/h                                                                         7.5      24.2     31.6                                       ethene kg/100 kg hexane                                                                        3.4      3.86     2.5                                        propene kg/100 kg hexane                                                                       11.0     12.0     6.8                                        ethylidene norbornene                                                                          0.65     0.74     .0156                                      kg/100 kg hexane                                                              VOCl.sub.3 catalyst m mole/hr                                                                  2.07     13.4     15.3                                       Al.sub.2 Et.sub.3 Cl.sub.3 cocatalyst                                                          12.4     80.6     92.1                                       m mole/hr                                                                     transfer agent ppm on ethylene                                                                 400      200      125                                        Cationic Agents                                                               EtAlCl.sub.2 m mole/hr                                                                         --       --       46                                         HCl              --       80.4     --                                         ______________________________________                                    

EXAMPLE II

The polymerization reaction of Example I was repeated in substantiallythe same manner using the conditions set forth in Run B of Table II.Although the polymer found had substantially the same Mooney Viscosityand thickening efficiency as the polymer of Run A, its bulk low strainrate viscosity was higher than the high molecular weight control (TableIII).

EXAMPLE III

The polymerization reaction of Example I was repeated using theconditions of Run C (Table II). Again an oil soluble polymer ofsubstantially lower T.E. is produced with improved SSI as compared tothe high molecular weight control (see Sample D of Table III below). Yetthe bulk viscosity is nearly as high as the high molecular weightcontrol. In this example EtAlCl₂ was used as the cationic initiatorwhereas HCl was used in Example II. If desired a promoter of thisinvention can be used with the EtAlCl₂. An analysis for unsaturationdetected 0.2 weight percent ethylidene norbornene. The polymer issubstantially saturated.

The polymers of this invention Run B (Example II) and Run C (ExampleIII) are compared to Run A (Example I) a low molecular weight polymer asa control, and a high molecular weight commercially availableethylene-propylene polymer as an additional control. The results areshown in Table III. The high molecular weight polymer exhibits poorshear stability (SSI=30%). While the low M.W. control (Run A) has a goodSSI value (18%), it has a low bulk viscosity (4×10⁵ poise). As a resultit can not be readily handled because of severe agglomeration problems.The polymer of Run B is substantially identical to the branched controlpolymer (Run A) except that its bulk viscosity is 1.3×10⁶, andtherefore, can be readily handled. It forms a crumb which remains asdiscrete particles for a time sufficient to empty the recovery vesseland complete polymer finishing and packaging. While the polymer of Run Chas a slightly higher SSI (23%) it is still acceptable.

The shear stability index (SSI) is determined by measuring the initialviscosity of the polymer subjecting it to sonic shear and then againmeasuring the viscosity. The percent change in viscosity, expressed as apercent value, is the SSI.

The thickening efficiency (T.E.) of the polymers of Runs A, B and C areall within acceptable limits. The polymers were tested for T.E.measurements by dissolving them in a solvent extracted neutral minerallubricating oil having a viscosity of 150-SUS at 37.8° C.

                  TABLE III                                                       ______________________________________                                        Comparison of Polymers                                                                  wt. %                                                                         ethyl-  Mooney        η.sub.o                                                                          SSI                                    Polymer   ene     100° C.                                                                         [η]*                                                                           poise  (%)  T.E.                              ______________________________________                                        A   low molec-                                                                              44      15     1.4    4 × 10.sup.5                                                                 18   1.8                                 ular weight                                                                   control                                                                   C   --        43      20     1.6  1.3 × 10.sup.6                                                                 23   2.2                             B   --        45      23     1.4  4.0 × 10.sup.6                                                                 18.5 1.9                             D   high molec                                                                              44      45     2.0    2 × 10.sup.6                                                                 30   2.8                                 ular weight                                                                   control                                                                   ______________________________________                                         *intrinsic viscosity in decalin at 135° C.                        

EXAMPLE IV

The experiment of Example II is rerun in the same manner except thatisobutene is fed to the reactor at the same rate as5-ethylidene-2-norbornene. The polymer has a bulk viscosity in excess of10⁷ poise at a strain rate of ca 10⁻³ sec at 100° C. There is less than1.5×10⁻³ moles unsaturation/100 g polymer.

It is not intended that the scope of this invention be limited by themethod of manufacture. While the Examples refer to a continuous flowstirred reactor, any method of polymerization suitable for ethylenecopolymer polymerization may be used. For example, a tubular reactor ofthe type utilized in the manufacture of polyethylene may be used.

In carrying out the polymerization of this invention in a tubularreactor, all of the catalyst system need not be introducedsimultaneously. The Ziegler catalyst can be introduced at the reactorinlet and the cationic initiator can be introduced downstream afterpolymerization has commenced.

As used in the specification and claims, the term "substantiallysaturated" means that the polymer has less than 5.0×10⁻³ moles ofolefinic unsaturation/100 g. polymer. Preferably the unsaturation levelis less than 10⁻³ moles/100 g of polymer.

The polymer prepared by the method of this invention are oil solublepolymers which are useful as viscosity modifiers. They may be used withany class of lubricating fluids in which they are soluble, either alone,or in conjunction with other oil additives. The term "lubricating fluid"as used in the specification and claims means naphthenic, aromatic orparaffinic petroleum oil fractions which are generally suitable for useas lubricating fluids as well as synthetic lubricating oils such aspolyesters, polyalphaolefins of C₅ -C₂₀ alphaolefins and C₁₀ trimers.The polymer of this invention are generally utilized in the lubricatingfluid at about 0.5% to about 5% by weight of the overall composition,preferably about 0.8 to about 1.5% by weight.

The polymers of this invention have a bulk viscosity which is at least 3times that of a linear ethylene-propylene polymer of the same intrinsicviscosity and ethylene content.

What is claimed is:
 1. A lubricating oil composition comprising alubricating fluid and an amount, effective for improving viscosity, of athickening agent which comprises a substantially saturated, long chain,branched ethylene tetrapolymer comprising ethylene, an alpha-olefin, anon-conjugated diene monomer having a first site of unsaturation whichis coordination catalyst polymerizable and a second site of unsaturationwhich is cationically polymerizable, and a cationically polymerizablemono-olefin; said monomer having a bulk viscosity at 100° C. and strainrate less than 10⁻³ sec⁻¹ which is at least 3 times that of a linearethylene-propylene polymer having the same intrinsic viscosity andethylene content.
 2. The composition according to claim 1 wherein thecationically polymerizable mono-olefin is isobutene.
 3. The compositionaccording to claim 2 wherein the alpha-olefin is propylene and thenon-conjugated diene is 5-ethylidene-2-norbornene.
 4. The polymeraccording to claim 3 wherein the isobutene and 5-ethylidene-2-norborneneare incorporated in equal molar quantities.
 5. The composition of claim1 wherein the alpha-olefin is a C₃ -C₁₈ alpha-olefin.
 6. The compositionof claim 5 wherein the alpha-olefin is a C₃ -C₈ alpha-olefin.
 7. Thecomposition of claim 6 wherein the alpha-olefin is propylene.
 8. Thecomposition according to claim 1 wherein the non-conjugated diene is2-methyl hexadiene-1,5; 2-methyl heptadiene-1,6;5-methylene-2-norbornene; 5-ethylidene-2-norbornene;5-(2'-methyl-1-propene)-2-norbornene; 5-methyl vinyl-2-norbornene;3-methallyl cyclopentane; 3(2'-methyl-1-propene)cyclopentene ordicyclopentadiene.
 9. The composition according to claim 8 wherein thenon-conjugated diene is 5-ethylidene-2-norbornene.
 10. The compositionaccording to claim 4 wherein the alpha-olefin is propylene and thenon-conjugated diene is 5-ethylidene-2-norbornene.
 11. The lubricatingoil composition according to claim 4 wherein the polymer is present atabout 0.5% to about 3% by weight of the composition.
 12. The lubricatingoil composition according to claim 11 wherein the polymer is present atabout 0.8% to about 2.0% by weight.
 13. A lubricating oil compositioncomprising a lubricating fluid and an amount, effective for improvingviscosity, of a thickening agent which comprises a substantiallysaturated, long chain, branched ethylene terpolymer consistingessentially of ethylene, an alpha-olefin, and a non-conjugated dienemonomer having a first site of unsaturation which is coordinationcatalyst polymerizable and a second site of unsaturation which iscationically polymerizable; said polymer having a bulk viscosity at 100°C. and strain rate less than 10⁻³ sec ⁻¹ which is at least 3 times thatof a linear ethylene-propylene polymer having the same intrinsicviscosity and ethylene content.
 14. The composition of claim 13 whereinthe alpha-olefin is a C₃ -C₁₈ alpha-olefin.
 15. The composition of claim14 wherein the alpha-olefin is is a C₃ --C₈ alpha-olefin.
 16. Thecomposition of claim 15 wherein the alpha-olefin is propylene.
 17. Thecomposition according to claim 13 wherein the non-conjugated diene is2-methyl hexadiene-1,5; 2-methyl heptadiene-1,6;5-methylene-2-norbornene; 5-ethylidene-2norbornene;5(2'-methyl-1-propene)-2-norbornene; 5-methyl vinyl-2-norbornene;3-methallyl cyclopentane; 3(2'-methyl-1-propene)cyclopentane ordicyclopentadiene.
 18. The composition according to claim 17 wherein thenon-conjugated diene is 5-ethylidene-2-norbornene.
 19. The compositionaccording to claim 13 wherein the alpha-olefin is propylene and thenon-conjugated diene is 5-ethylidene-2-norbornene.
 20. The lubricatingoil composition according to claim 13 wherein the polymer is present atabout 0.5% to about 3% by weight of the composition.
 21. The lubricatingoil composition according to claim 19 wherein the polymer is present atabout 0.8% to about 2.0% by weight.